The transport of lipophilic materials through aqueous plasma in animals is accomplished by serum lipoproteins. The critical role of lipoproteins in mediating a balance between physiological lipid transport needs and hyperlipidemic disease is well established. However, a better understanding of the physical basis of lipid transport via lipoproteins is needed. In insects, a single lipoprotein, lipophorin, functions as the major lipid transport vehicle. This lipoprotein undergoes remarkable transitions during the life cycle to meet the changing physiological needs. A specific hormone induced lipophorin transition from high to low density provides a model system for physical studies of lipoprotein metabolism in general. The metabolic events surrounding lipid loading and apoprotein association together with the interaction of lipophorin with a specific flight muscle lipase will be examined in pursuit of the following specific aims: 1. Time course and sequence of low density lipophorin formation 2. Mechanism of diacylglycerol transfer from fat body tissue to lipophorin 3. Interaction of low density lipophorin with flight muscle 4. Role of apolipophorin III as a recognition signal/activator for low density lipophorin lipase. Due to the relative simplicity of this insect system, a detailed understanding of lipoprotein metabolism is possible. The data obtained should provide basic information about lipoprotein metabolism in general that should relate to higher animals.